In recent years, molecular biology and tumor pharmacology studies have shown that tyrosine kinase (Protein Tyrosine Kinases, PTKs)-related cell signal transduction pathways play an extremely important role in tumor formation and development, and that more than 50% of proto-oncogenes and oncogene products have tyrosine kinase activity. The c-Met proto-oncogene belongs to the Ron subfamily of the PTKs family, and the encoded c-Met protein is a high affinity receptor for the Hepatocyte Growth Factor/Scatter Factor, HGF/SF. The HGF/c-Met signaling pathway is closely related to the process of angiogenesis and tumor growth. Its sustained activation is an important cause of carcinogenesis, cancer cell proliferation, or hyperplasia of cancer cells. Inhibition of this pathway has become a new method of targeted tumor therapy.
The c-Met proto-oncogene, which is more than 120 kb in size is located on the long arm of human chromosome 7 (7q31), and it encodes a c-Met protein precursor with a molecular weight of about 150 kD, which undergoes local glycosylation to form a 170 kD glycoprotein. The glycoprotein is further cleaved into an alpha subunit (50 kDa) and a beta subunit (140 kDa), which are linked by disulfide bonds to form a mature c-Met protein receptor. The heterodimer contains two strands, the beta chain has an extracellular domain, a transmembrane region (also called a membrane stretch fragment), and an intracellular domain (comprising an intracellular tyrosine kinase binding site). The alpha chain has only an extracellular portion, but it is highly glycosylated and is attached to the beta chain by disulfide bonds. The extracellular region of the two subunits is the recognition site of the corresponding ligand, and the intracellular domain has tyrosine kinase activity.
C-Met activation occurs through three types of mechanisms: one type is dependent on the activation mechanism of HGF, the second type is not dependent on the HGF activation mechanism, and the third type occurs through other membrane pathways, such as through the hyaluronic acid surface receptor CD44, adhesin and RON signal transduction pathways, and so on. One of the most common mechanism of c-Met activation is that dependent on the activation mechanism of HGF. The N-terminus of HGF binds to c-Met to promote the dimerization and autophosphorylation of Tyr1234 and Tyr1235 on the beta chain, and phosphorylation of Tyr1349 and Tyr1356 near the C-terminus produces a binding site for multiple linker proteins which in turn induce P13K/Akt, Ras/Mapk, c-Src and STAT3/5-mediated activation of downstream signaling, and trigger different cellular responses, such as cell survival and activity (closely related to P13K/Akt pathway) and tumor metastasis and cell proliferation (mainly mediated by Ras/Mapk). In addition, the cross-talk of c-Met with other membrane receptors has been known to promote tumor formation and metastasis. Since c-Met is the intersection of many pathways leading to tumor formation and metastasis, simultaneous interference with many pathways can be achieved relatively easily by targeting c-Met, and c-Met has become a promising target for antitumor formation and metastasis therapy.
An antibody drug conjugate (ADC) is formed by linking a monoclonal antibody or antibody fragment to a biologically active cytotoxin with a stable chemical linker, which fully utilizes the specific binding activity of the antibody to a tumor cell or a highly expressed antigen, combined with the high efficiency of the cytotoxin, to avoid toxic side effects to normal cells. This means that antibody drug conjugates can bind tumor cells specifically and reduce their effects on normal cells, compared to conventional chemotherapeutic agents.
ADCs consist of three parts: antibodies (targeting), linkers and toxins. Among them, a good target (antibody portion), which includes not only specific targeting binding, but also effective endocytosis, determines the specificity of the ADC drug.
There are three main types of inhibitors for c-Met kinase: HGF and c-Met biological antagonists, HGF and c-Met antibodies, and small molecule c-Met inhibitors. The existing clinical studies show that the antibodies directly targeting HGF or c-Met, or c-Met small molecule inhibitors is not ideal. An ADC for c-Met may be the most effective method for treating a tumor. Presently, there is no c-Met ADC drug in clinical studies.
The present invention firstly discloses an anti-c-Met ADC, which not only retains the antibody-dependent cell proliferation inhibitory effect of the anti-c-Met antibody of the present invention, but also increases the effect of the potential cytotoxic drug. Because of the targeted release of toxin into tumor cells, toxic drug side effects do not increase with the increase in efficacy. The present invention provides a humanized antibody and a chimeric antibody that specifically bind human c-Met, and the humanized antibody and chimeric antibody are characterized by high affinity, high efficacy, endocytosis, good stability and absence of c-Met agonist activity, etc. On the basis of these desirable properties, the present invention also provides an antibody-cytotoxic drug conjugate that specifically binds to human c-Met, or a pharmaceutically acceptable salt or solvate compound thereof, that retains the antibody-dependent inhibition of cell proliferation while increasing the potential effect of the conjugated cytotoxic drugs and the broad spectrum of diseases that can be treated by the conjugate. Because the toxin is releases into targeted tumor cells upon endocytosis of the anti-c-Met antibody of the present invention, the toxic drug side effects do not increase along with the increase in efficacy.